1. Field of the Invention
The present invention relates to a hermetically sealing enclosure for housing photo-semiconductor devices and other related devices (hereinafter collectively referred to as photo-semiconductor devices). More specifically, it relates to a hermetically sealing enclosure for housing electronic devices (such as optical devices, optical fiber amplifiers equipped with semiconductor ICs, and excitation light sources) that require electrode terminals to have a current-carrying capacity at least two times that of the conventional devices. It further relates to a photo-semiconductor module incorporating the enclosure.
2. Description of the Background Art
FIG. 6 shows a typical example of a conventional hermetically sealing enclosure for housing photo-semiconductor devices. The enclosure comprises (a) a metal base plate 1 that is made of a copper-tungsten alloy and that has at the central portion of its top side an area for mounting photo-semiconductor devices, (b) a side-frame member 2 that is made of an iron-nickel-cobalt-family alloy and that is brazed on the metal base plate 1 such that it encloses the area for mounting photo-semiconductor devices, (c) a means for securely holding an optical fiber at the front side frame of the side-frame member, (d) ceramic terminal members 3 that are incorporated into the side-frame member and that are provided with metallized wiring strips onto which external leads 4 made of an iron-nickel-cobalt alloy are connected, and (e) a seal ring 5 that is brazed on the planar surface produced by the top surface of the ceramic terminal member 3 and the top surface of the side-frame member 2 to form a metal frame for hermetically sealing the enclosure.
The assembly of a photo-semiconductor module is usually completed as a unit by the following process using the above-described enclosure: (a) Electronic devices such as photo-semiconductor devices and thermoelectric coolers are mounted in an area for mounting these devices on the metal base plate. (b) The electrodes of these devices are connected by bonding wires to the metallized wiring strips to which the external leads are connected. (c) The optical fiber is bonded to an optical fiber-fixing ring at the front side frame of the side-frame member by yttrium-aluminum-garnet (YAG) laser beam welding. (d) A seal cover is placed on the top surface of the sealing ring to hermetically seal the enclosure.
The ceramic terminal member is formed by firing at least two laminated layers of ceramic preforms. The electrical continuity between the inside and outside of the enclosure can be provided by printing the metallized wiring strips on the surface of the ceramic preforms in advance. The metallized wiring strips are made of a high melting-point metal such as tungsten, molybdenum, or manganese.
The enclosure is required to have the following two principal features: (a) It must effectively dissipate the heat generated during the conversion of optical signals to electrical signals and vice versa. (b) It must have a particular structure such that its thermal distortion cannot cause misalignment in the optical axis between the optical fiber and the photo-semiconductor device. It is well known that in order to effectively dissipate the heat, a thermoelectric cooler is placed directly underneath the photo-semiconductor device, and highly heat-conductive materials are used for the members constituting the enclosure.
Such an enclosure and a photo-semiconductor module incorporating the enclosure have been disclosed, for example, by the published Japanese patent application Tokukaihei 11-145317. The enclosure disclosed in this application has the following structure to suppress the generation of thermal distortions. (a) The main body of the enclosure is formed by combining a metal base plate with a side-frame member having a front side frame at which a means for securely holding an optical fiber is provided. (b) Part of the upper portion of the side-frame member is cut out to provide a space for a ceramic terminal member that is composed of at least two ceramic layers and that is provided with metallized wiring strips. (c) The ceramic terminal member is placed in the space such that its one end in the longitudinal direction is in contact with the inner surface of the front side frame and its opposite end is exposed to produce a surface flush with the outer surface of the rear side frame. (d) A metal seal ring is placed on the planar surface produced by the top surface of the ceramic terminal member and the top surface of the side-frame member.
As described above, the heat dissipation of a hermetically sealing enclosure for housing photo-semiconductor devices thus far has been dependent on design concepts such as the selection of the constituting materials. Conventional enclosures have ceramic terminal members provided with metallized wiring strips having relatively high electrical resistance. This relatively high resistance causes insignificant problems because of the small amount of the heat generated by the current flowing the resistance. However, recent technical developments have increased the output of the laser diode (LD) for optical fiber amplifiers and excitation light sources. As a result, a thermoelectric cooler for cooling an LD requires an operating current at least two times that of the conventional cooler. In the conventional cooler, the current is at most about two amperes and generates a negligible amount of heat. However, the current increased by a factor of at least two generates a non-negligible amount of heat. More specifically, the increased current not only increases the power consumption but also increases the temperature rise in the metallized wiring strips to the extent that it cannot be neglected. This temperature rise in turn increases the resistance of the metallized wiring strips. This resistance increase has given rise to various problems such as causing difficulty in the operational controll of the thermoelectric cooler, the reliability reduction in the wiring strips, and the reduction in the optical output of the LD due to its heat transfer.
The electrical resistance of the wiring strips formed in the body of the ceramic material can be reduced by using a metal having an electrical conductivity higher than that of tungsten and other high melting-point metals. However, this method increases the difference in the coefficient of thermal expansion between the ceramic material and the wiring strips, posing a problem of crack generation in the ceramic material. The electrical resistance can also be reduced by increasing the thickness of the wiring strips. This method, however, produces gaps in the ceramic material at the time of the firing of the ceramic preforms, preventing complete hermetic sealing. The electrical resistance can also be reduced by increasing the width of each wiring strip formed both on the surface of the ceramic material and in the body of the ceramic material. However, it is difficult to increase the width sufficiently because of problems such as the poor insulation between the neighboring wiring strips and the reduction in the number of wiring strips.
In order to solve the above-described problems, an object of the present invention is to offer a hermetically sealing enclosure for housing photo-semiconductor devices that has the following features: (a) The electrical resistance of the metallized wiring strips provided at the ceramic terminal member is reduced. (b) The heat generated in the wiring strips is reduced. (c) The wiring strips allow a larger current to flow than that allowed by the conventional enclosures while maintaining low power consumption. (d) The stable output of the device inside the enclosure is maintained. Another object of the present invention is to offer a photo-semiconductor module incorporating the enclosure.
The hermetically sealing enclosure of the present invention has the following components:
(a) a base plate having an area for mounting photo-semiconductor devices;
(b) a side-frame member bonded on the base plate such that the side-frame member encloses the area for mounting photo-semiconductor devices;
(c) a ceramic terminal member incorporated into the side-frame member such that the top surface of the ceramic terminal member and the top surface of the side-frame member produce a planar surface;
(d) a first wiring layer that:
(d1) comprises a plurality of wiring strips; and
(d2) penetrates through the ceramic terminal member;
(e) a second wiring layer (hereinafter referred to as the second wiring layer) that:
(e1) comprises at least one wiring strip;
(e2) is connected to the first wiring layer on the outside of the ceramic terminal member; and
(e3) stretches upward;
(f) another second wiring layer (hereinafter referred to as the other second wiring layer) that:
(f1) comprises at least one wiring strip;
(f2) is connected to the first wiring layer on the inside of the ceramic terminal member; and
(f3) stretches upward;
(g) at least one third wiring layer that:
(g1) comprises at least one wiring strip;
(g2) connects the second wiring layer and the other second wiring layer;
(g3) penetrates through the ceramic terminal member via a pathway insulated from the first wiring layer; and
(g4) is insulated from the other third wiring layers when more than one third wiring layer is used;
(h) a means for securely holding an optical fiber, the means being provided on the side-frame member;
(i) a seal ring placed on the planar surface produced by the top surface of the ceramic terminal member and the top surface of the side-frame member;
(j) a sealing cover placed on the top surface of the seal ring; and
(k) a plurality of external leads connected to the wiring strips in the first wiring layer at the outside of the enclosure.
In an embodiment of the present invention, the external leads include at least one external lead (hereinafter referred to as an external lead AA) having a thickness larger than the distance between the first wiring layer and the third wiring layer or the uppermost third wiring layer. The external lead AA or each external lead AA is connected to a wiring strip in the first wiring layer, the wiring strip being connected to a wiring strip in the second wiring layer. The external lead AA or each external lead AA is connected to the third or every third wiring layer.
In another embodiment, the external leads include at least one external lead (hereinafter referred to as an external lead BB) having the shape of the letter L. The external lead BB or each external lead BB is connected to a wiring strip in the first wiring layer, the wiring strip being connected to a wiring strip in the second wiring layer. The bent shorter portion of external lead BB or each external lead BB has a length larger than the distance between the first wiring layer and the third wiring layer or the uppermost third wiring layer and is connected to the third or every third wiring layer.
In yet another embodiment, the enclosure is provided with, at its inside, at least one metal part having the shape of the letter L. A bent portion of the metal part or each metal part is connected to a wiring strip in the first wiring layer, the wiring strip being connected to a wiring strip in the other second wiring layer. The remaining straight portion of the metal part or each metal part has a length larger than the distance between the first wiring layer and the third or the uppermost third wiring layer and is connected to the third or every third wiring layer.
The above-described external leads and metal parts having the shape of the letter L are made of oxygen-free copper, a copper matrix in which alumina is dispersed, or a clad material in which copper is sandwiched between iron-nickel-cobalt alloys.
The photo-semiconductor module of the present invention comprises the above-described hermetically sealing enclosure for housing photo-semiconductor devices.